While playing the Flow tracks recently I noticed considerable variability in the sound quality, most especially in the treble spectrum.  While I appreciate that some recordings were made years ago and others more recently, can this fact alone account for such a clear difference? It became so clear that many of the tracks suggested sounded like they were recorded in a box of cotton wool, very muffled - and not worth the cost of bothering with an HD version in my view. Without changing anything, the next track sounded clear and crisp.

Appreciate any thoughts, experience or comment on this.